Bob Carr knows a thing or two about the perils of not keeping one's mouth shut.

Two weeks out of parliament, though, and it seems the retired Labor senator is relishing the chance to tell us what he really thinks.

The former NSW premier and ex-foreign minister appeared at Sydney's Opera House on Monday alongside deposed press baron Conrad Black to share a frank view of the US and its relationship with Australia.

Mr Carr recalled raising a few eyebrows last year, when he was still a 'modest Australian foreign minister — which is to say, an Australian foreign minister'.

He told the United States Studies Centre's Public Knowledge Forum he made global headlines with a throw-away comment to then-US presidential hopeful Mitt Romney to the effect that the US was one budget deal away from banishing speculation about American decline.

'My comment, which I thought was entirely unexceptional — just a polite thing to say to keep the conversation going — was taken up by lots of other people, and by (former World Bank boss Robert) Zoellick,' he said.

If it taught him a lesson about diplomacy, he seemed to push it to the back of his mind on Monday.

The US-led wars in Iraq were 'ungainly, expensive, draining', Mr Carr declared; and Fox News was full of 'fire-breathing, table-thumping' personalities who forced Republican politicians so far to the right as to deny them a shot at the White House.

'As a surrogate Democrat, I can see that Fox News is working almost as a laboratory experiment to render the Republican party unelectable at each presidential election,' Mr Carr said.

'It's just fantastic.'

And the one-time journalist bemoaned what he sees as the dwindling fortunes of the media.

'I'm a bit of a pessimist because the newspapers train people, (and) newspapers are going into decline,' he said.